A brouter is a networking device that includes the functions of a bridge (transfer of individual network protocol data units between two parts of a network) plus some functions of a router (e.g., forwarding or blocking packets between two media).
A brouter is often used in a local area network (LAN) to transfer a packet between two different media, particularly where one of the media types is wireless (i.e., Infrared or radio frequency). For example, a brouter may be used to transfer a packet from a wireless medium, such as an infrared (IR) remote control, to a wired medium, such as coaxial cable, or vice-versa. Brouters are used for connecting wired and wireless media because of considerations that are unique to wireless media (e.g., a single source transmission may result in multiple receptions at multiple entry points into the network). The brouter includes suitable physical layer and link layer communications functions that are unique to each respective medium over which the data are transferred.
In a typical conventional LAN configuration, as shown in FIG. 16, a brouter 600 and a group of devices 604-609 are each connected to a wired LAN medium 620. Each of the devices 604-609 has a respective transceiver 602a-602f for interfacing to the LAN medium 620. The brouter 600 connects to the LAN medium 620 and to a second medium 630, such as IR or RF. A wireless device 640 transmits packets to brouter 600. Incoming packets from the IR or RF medium 630 are received by the brouter and are transferred to a destination device 604-609 by way of the wired LAN medium 620. This configuration uses a plurality of network interfaces (e.g., transceivers) 602a-602f. This configuration also results in network traffic loading each time a packet is transferred between the wireless medium 630 and the wired medium 620.
As an example, a relatively new use for brouters is in the "smart home". In recent years, an increasing number of automated appliances and devices have been developed for home use. These include, but are not limited to, entertainment systems, washers, dryers, security and temperature control systems for air and hot water. The potential exists to provide communications among these appliances and devices.
The CEBus standard is a home automation standard intended to provide economical Local Area Network (LAN) communications among all of the automated devices within the home. CEBus supports remote control, status monitoring and clock synchronization. CEBus is defined in Electronics Industries Association EIA/IS-60, "Home Automation Standard (CEBus)", December, 1989. The CEBus protocol is also described in "Delay Performances of Standard and Modified CEBus Schemes", by A. Hussain et al. in IEEE transactions on Consumer Electronics, Vol. 38 Number 2, May, 1992, at pp. 77-79, and "Investigation of the Performance of a Controlled Router for the CEBus", by J. Yang et al., IEEE transactions on Consumer Electronics, Vol. 38 Number 4, November 1992, at pp. 831-832. The teachings of these two articles are hereby incorporated by reference for their teachings on CEBus. The CEBus Protocol is designed to provide communications between any devices on any of the physical media that support CEBus. These include power line, twisted pair, coaxial cable, Infrared (IR), radio frequency (RF) and Fiber Optic.
The CEBus standard employs a carrier sense multiple access protocol with contention detection and contention resolution (CSMA/CDCR). CEBus is based on the International Standards Organization's Open System Interconnect (ISO/OSI) seven layer model for communications. CEBus uses only four of the seven layers: the physical, datalink, network and applications layers. The physical layer supports a superior (driven) state and an inferior (not driven) state. Symbols are represented by pulse width encoding, so that the length of time between a transition of the carrier signal (e.g., high to low or low to high) defines the symbol. A 100 microsecond duration between transitions (the Unit Symbol Time or UST) represents a one; two UST's represents a zero; three UST's represents an end of file (EOF); and four UST's represent an end of packet (EOP). Another distinguishing feature of CEBus is the structure of the data link frame header, which includes a preamble, a control field, a destination address, a destination house code, a source address, a source house code, an information field and a frame check sum.
CEBus networks are typically implemented in dynamically reconfigurable tree (hierarchical) structures, so that there is a unique path between each pair of devices. As a result of this hierarchical topology, the networking device that transmits a packet need only determine whether to forward a packet to the next medium. The networking device need not perform the full suite of networking services (e.g., choosing one of several available paths between source and destination) that are required in mesh type networks. Furthermore, duplicate copies of packets are not created (with the exception of some systems using wireless media), so that the networking device need not sort out and discard duplicate packets. Because of the simplified routing in CEBus networks, the networking device of choice is often a brouter.
A typical application of CEBus is the transmission of a control signal from a digital IR remote control device to an audio visual component that is connected to a wired LAN medium (e.g., coaxial cable). A brouter may be connected to the LAN to be used as a wireless receiver to forward packets in either direction between the wireless IR medium and the wired LAN medium. Typically any of the devices (the brouter and the audio visual devices) connected to the wired LAN can communicate with any other device connected to the LAN by way of the wired medium. Commands from the IR remote control are received by the brouter and routed over the wired medium to the device that is being controlled.
For the configuration described above, each audio visual component has a respective network interface (e.g., a transceiver) which allows it to communicate over the wired LAN. Thus, in the typical application, costs are incurred for several network interfaces. Each time a command is transmitted from the remote control to an audio visual device, the command is routed over the wired LAN medium. This increases the network traffic load and may result in increased packet delay.
Although CEBus is designed to advance home automation by an order of magnitude, CEBus has not been installed widely in homes. Part of the reason is the interface cost between the devices and the communications medium. To make the "smart home" a reality, less expensive equipment is needed to connect consumer devices to CEBus LANs. Communications among equipment using other media may also be impacted by this problem.
A cluster controller or concentrator is a device that provides an interface for a plurality of devices (e.g., terminals) that are coupled to a processor or network. Instead of providing a network interface for each device, a single network interface is provided for the cluster controller. This simplifies the hardware for connecting the devices to the network or processor, and increases the efficiency of the processor communications; the processor need only communicate with a single physical device, the cluster controller. An example of a cluster controller is an IBM 3174 Establishment Controller.
Although cluster controllers enhance efficiency, the services they provide are limited to communications between the devices (e.g., terminals) and the processor or network. A cluster controller does not provide communications among the attached devices. For example, if two terminals are attached to a cluster controller and a message is to be passed between the terminals, the message is sent from the sending terminal through the cluster controller to the processor, and back from the processor through the cluster controller to the receiving terminal.